Life Cycle Assessment on fiber cable construction methods
The demand for effective and high-speed telecommunication is growing fast in line with developments in modern society. Old telecommunication infrastructure, based on copper cable networks, cannot supply this increasing demand. Fiber optic network has been developed as a proper solution due to its vastly higher capacity for information transmission than that of copper based networks. As a result for need of faster and more economical construction methods, new fiber construction methods have been developed as well. Some conventional fiber network construction methods (E.g. Conventional Excavation, Chain Excavator, and Ploughing) have previously been studied using Life Cycle Assessment (LCA) but no study on new methods (E.g. Micro Trenching, Narrow Trenching) with life cycle perspective has been performed yet. Construction of fiber cable networks requires high energy and material use. Building and construction are energy and material demanding processes, which have obvious effect on the environment, therefore conducting an LCA study on newer construction methods is necessary to be able to identify hotspots and to provide basis for choice of the most environmentally friendly construction method when developing fiber network. The three main phases of each construction method (excavation, laying, and recovery) and the related processes were included in the assessment of the present study. Due to different ground conditions and different applications of Swedish legislation regarding the reuse of the excavated mass, two different scenarios were modeled; with and without reuse of excavated mass in recovery phase as backfilling mass.
The results of the LCA study showed that the recovery phase generally stands for the largest environmental impacts in all impact categories for all construction methods. The magnitude and the reason for this impact are different for construction methods applied on asphalt and on green space. In methods applied on asphalt without reuse of the excavated mass, the reason is impacts from asphalt production and transportation of excavated masses to treatment/recycling plant and of new filling material. In case of the excavated mass reuse, the difference between impact from recovery and other phases is much smaller, but still recovery has larger impact due to involved asphalt paving stages. For construction methods applied on green space recovery phase has largest impact as well, but the difference between impact from this phase and other phases is not as significant as in methods applied on asphalt. The main reason for large impact in recovery phase in two methods (Conventional Excavation in Green space and Chain Excavator) applied on green space is transportations of excavated mass to recycling and new filling material. However, specifically in case of Chain Excavator excavation phase had a large impact as well due to high fuel required for operating the machine. The third method in this group i.e. Ploughing is a simple method where no transportation of excavated mass and new filling mass are included.
A separate analysis on two methods with least environmental impacts between methods applied on asphalt was made focusing on only machinery, where material (Asphalt, gravel, and sand) and transportations were excluded in the model. The results showed that even in this situation recovery phase stands for biggest impacts in most of categories, but excavation phase has also a considerable contribution to the total impacts. In this regard, improvements in machinery use in both excavation and recovery phase by streamlining included processes can be done in order to minimize the total environmental impacts in each construction method.
Waste management of asphalt was excluded from the main system studied due to complexity of the issues and the lack of data. However, sensitivity analysis was done by including a waste management scenario for asphalt recycling using reclaimed asphalt pavement for mixing with virgin asphalt. The results showed the importance of impacts from asphalt production. After expansion of the model and calculating the avoided burden of asphalt, a saving (Avoided environmental load when recycling instead of producing the same amount of virgin asphalt) for Conventional Excavation in Asphalt was observed, but due to high uncertainty regarding data in this part no more detailed conclusions can be drawn in this case. However, no saving for Micro Trenching and Narrow Trenching was observed. The reason was that negative impact from transportations was larger than positive impact from recycling through saving in less production of virgin asphalt.
Based on the results of the study it can be concluded that for the construction methods to be as environmentally friendly as possible it is important to avoid asphalt surfaces for fiber cable network construction if possible. Between the construction methods applied on green space the method with the least potential environmental impact is ploughing, in which the total generated amount of CO2 eq for construction per functional unit is 10.2 kg. If it were not possible to avoid asphalt, the construction methods with smallest excavated mass e.g. Micro Trenching and Narrow Trenching, in which the total amount of CO2 eq is respectively 152 kg and 239 kg for construction per functional unit, would be the most environmental option from a life cycle perspective. Innovations in asphalt production, such as using biofuel and renewable energy sources for heating and mixing processes in asphalt production, may decrease the environmental impact of asphalt and there with the impact of the construction methods applied on asphalt. Other processes with the significant environmental impact are transportations and asphalt paving for the construction methods applied on asphalt, and excavation and transportations for the construction methods applied on green space.
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